2. Field of Invention
The present invention is directed toward improved methods and media for use in apparatus utilising the combined effect of at least two intersecting beams of radiation.
2. Description of the Prior Art
Known media for this purpose have been described in U.S. Pat. Nos. 3,609,706 and 3,609,707 and 4,041,476. These patents are incorporated herein by reference. Part of the last named application appears as British Pat. No. 1,243,043.
In general the known media may require a substantial period of time for use in the construction of extensive or elaborate shapes, sometimes there is undesireable sensitivity or residual sensitivity to one or more of the activating beams, which restricts use to construction of certain simple shapes.
In the above mentioned U.S. Pat. No. 4,041,476 media suitable for use in the invention are grouped into two classes. These classes describe the relationship between the constructing beams and the elements of the medium which form the active region in response to the combined effect of the at least two beams. It may be noted that the two classes relate to the micro-scale of the reactive systems and are not descriptive of the manner in which the constructing beams are manipulated. Manipulation of the beams may be identical whichever class is used.
Class I systems are those in which the effect of the two beams in generating the active region occurs through their simultaneous action. For example, two components may be incorporated within the medium which are both light sensitive but to different spectral regions. By intersecting in the volume two beams of corresponding wavelength each will produce its light-produce in parallel reactions and the two products simultaneously present in the given region will react to form the desired sensible object. When one or both of the products undergoes rapid reverse reaction (as is desirable in order to avoid interference effects) no sensible object will be generated where the two beams are not simultaneously present.
Class II systems differ from the former in that the medium in the first instance contains only a single reactive component which must be stimulated by a first of at least two beams (designated the primary beam), to thereby generate a second component which is sensitive to the second or secondary beam. By this sequential process Class II media provide the active region which generates the sensible object. Additive systems such as shown in Example 3 of U.S. Pat. No. 4,041,476 in which the beams are identical have characteristics common to both Class I and Class II, in that they work by the cumulative effect of both simultaneous and sequential reactions. In this case the products of reaction in the active region accumulate at a rate greater than the rate of accumulation in other regions or individual beam paths. Such systems can be successfully used with an effectively infinitive number of intersection beams produced by a lens focus or many individual beams, but they are inferior to other systems.
The prior art has disclosed a variety of optical memory devices, such as the article by Stephen Herman presented at the Symposium on Modern Optics, Polytechnic Institute of Brooklyn, March 1967, and reprinted in Modern Optics. All of such devices have been two-dimensional arrays with the exception of that described by Geller in U.S. Pat. No. 3,654,626.